1227747 with DEKA injectors

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03-13-2019
bp71k5

1227747 with DEKA injectors

Hi there,

I'm using the Affordable Fuel Injection TBI injector tree which is using 2 Deka 840cc@43.5 psi injectors. (80#)

I'm using a BPW spreadsheet to calculate what my BPW should be and it gives me ~134 which is close to the BPW I see in most of the stock bins for a relatively stock GM 7.4L. I'm running a moates emulator to start the engine and I can only get the engine to idle with 165 BPW, 65 psi, and the fuel table in the 50% range. This doesn't quite seem right given that many of these engines seem to do fine with 80lb injectors running with much less fuel pressure. It just seems to want much more fuel than expected and make me think something is not right.

I wonder if there are some injector settings in the BIN that I might be overlooking given that these injectors are quite different than the originals? I see posts about injector voltage bias, and PW, but am not familiar enough with those to know if that's what I need to adjust.

Appreciate any pointers.
Brian
03-14-2019
dave w

Is this what you have? See link: https://www.ebay.com/i/252865497725?chn=ps

Seemingly AFI should have the injector parameters you need? I can't imagine why AFI would not have the parameters you need?

dave w
03-21-2019
Freak

Quote:

Originally Posted by dave w

Is this what you have? See link: https://www.ebay.com/i/252865497725?chn=ps

Seemingly AFI should have the injector parameters you need? I can't imagine why AFI would not have the parameters you need?

dave w

AFI can provide tuners with the injector characteristics required for your calibration.....
03-21-2019
bp71k5

Quote:

Originally Posted by Freak

AFI can provide tuners with the injector characteristics required for your calibration.....

i did get some info, but I’m not sure if it is directly applicable to the 7747 ECM. I’ve been able to make some guesses on which data can be directly input into tunerpro. I’m not a total noob with tuning but I somewhat am in this case.

Theres a voltage offset set and what looks like a minimum pulse width. I guess I could directly ask if they have any mapping available for the 7747. Seems like such an obvious question now that I think about it. Here’s what I did find for info:

http://www.siemensdeka.com/wp-conten...t-Brochure.jpg
03-22-2019
dave w

Interesting Data in the link above.

Injector flow is based on 300 Kilo Pascals = 43.5 PSI = 80 lb/hr. Factory TBI injectors flow is based on 13 PSI

Perhaps the Base Pulse Width (BPW) needs re-calculated with 43.5 PSI fuel pressure?

Deka Injector Impedance = 12 Ohms. Factory TBI injectors are about 2 Ohms of Impedance.

The 1227747 Injector Driver (electronics) might not be a good match for the 12 Ohm Impedance Deka Injector?

dave w
03-22-2019
bp71k5

Quote:

Originally Posted by dave w

Deka Injector Impedance = 12 Ohms. Factory TBI injectors are about 2 Ohms of Impedance.

The 1227747 Injector Driver (electronics) might not be a good match for the 12 Ohm Impedance Deka Injector?

dave w

That’s entirely possible. By changing the injector pulse width vs voltage and minimum injector pulse width to that on the chart I’ve gotten it to run OK above idle (BLM’s in closed loop are able to be adjusted to stay around 128) Now the idle doesn’t want to settle down below about 1000 RPM and the IAC count is over 100. I’m wondering if the minimum pulse width or injector bias is a little too much and maybe I should turn that down to see if I can get less fuel at idle?
03-22-2019
1project2many

The chart appears to show minimum PW at 1.7 ms. I don't believe I'd go lower.
The voltage offset chart is also present at the link above. Having the correct voltage offsets is very important for consistent idle.
03-22-2019
bp71k5

Quote:

Originally Posted by 1project2many

The chart appears to show minimum PW at 1.7 ms. I don't believe I'd go lower.
The voltage offset chart is also present at the link above. Having the correct voltage offsets is very important for consistent idle.

I had the same thought so I did experimently lower the injector bias from 1.4 to 1.0 and it won’t idle at any temperature so I’m hoping there’s a sweet spot around 1.2. Or lower the fuel pressure a bit and hope I don’t lose too much fuel at the top end.
03-22-2019
bp71k5

Quote:

Originally Posted by bp71k5

I had the same thought so I did experimently lower the injector bias from 1.4 to 1.0 and it won’t idle at any temperature so I’m hoping there’s a sweet spot around 1.2. Or lower the fuel pressure a bit and hope I don’t lose too much fuel at the top end.

On second thought, I’m not sure what’s going on. When engine is cold, it’ll start up ok and then die unless I give it throttle. That seems to tell me it needs more fuel at idle.

Once it warms up it would idle, but too high with too high IAC counts.

Since the openloop AFR fueling level is set from the VE1 table and then adjusts the AFR to be richer during a cold start, there would have to be a very large fueling difference needed between cold and normal operating temperature, a larger difference than the openloop AFR vs coolant table is asking for. Is that a logical conclusion? It’s hard to believe changing the injector bias from 1.4 to 1.0 would expose that large of a cold vs hot fuel requirement difference.
03-22-2019
dave w

It might be a good plan to include a Wide Band O2 Sensor (WBO2) to the information collection process.

One possible option for a WBO2: https://www.aemelectronics.com/produ...uego-afr-gauge

dave w
03-22-2019
bp71k5

Quote:

Originally Posted by dave w

It might be a good plan to include a Wide Band O2 Sensor (WBO2) to the information collection process.

One possible option for a WBO2: [url]https://www.aemelectronics.com/products/wideband-uego-air-fuel-controllers/digital-wideband-uego-afr-gauge/digital-wideband-uego-afr-gauge[/url

dave w

That’s not a bad option for the price. May be time to do that.
03-22-2019
brian617

Quote:

Originally Posted by dave w

Deka Injector Impedance = 12 Ohms. Factory TBI injectors are about 2 Ohms of Impedance.

The 1227747 Injector Driver (electronics) might not be a good match for the 12 Ohm Impedance Deka Injector?

dave w

I'm with Dave here, has this been proven to work with 7747 or 7427 ECM/PCMs?
03-23-2019
bp71k5

There is a big difference in impedance, but I’m not convinced yet that it won’t work. It’s somewhat fun experimenting.

I did increase the injector bias back up to 1.2 and adjusted the minimum air setting and tried again but then the fueling was almost 20% too lean so after increasing that it’s idling pretty well now. IAC floats around 16. I did find a scalar called “IAC kick down steps” what’s supposed to be set to one digit higher than the idle IAC count. I’m wondering if that was my real problem earlier rather than being too rich at idle.

I still need to check the cold start again tomorrow and do some data logging but the 30-40 kpa VE table looks pretty close up to 3200rpm and the engine starts right up and idles where it should so I’m hopeful.
03-26-2019
bp71k5

I did hear back from AFI, and got some default injector offset table which puts the BPW number close to expected at 134 even with the lower 45psi fuel pressure. So far so good in that it starts up and idles reasonably well. Hoping for some time to datalog and tune in the fueling table.
03-31-2019
bp71k5

Just as a follow up in case anyone else is using these injectors, AFI gave me an injector flow chart similar with what I posted up above and a recommended BPW calculation along with a minimum pulse width of 2ms. So far seems to working fairly well. Got plenty of fuel at the top end and idles well now. It sure why I didn’t think to just ask for the data in the first place. Thanks for all the pointers in the right direction.
04-02-2019
1project2many

Excellent. Thanks for posting the conclusion.